The Least-Common-Denominator is really least-y....

Always interested in writing better code, I was perusing this
C++
Portability Guide for Mozilla developers.

The best recommendations for writing C++ code that will compile
on most C++ compilers include:

Don't use exceptions

Don't use the standard template library

Don't use namespaces

Some compilers require that variables which need a
constructor or initializer be declared at the start
of the method

Don't inline functions in the expression for a return value

You can drive my car, but I'd prefer that you not use the anti-lock
brakes, seat belts, air bags, cup holders, rear-view mirror, sun
visor, cassette deck, seat adjustments, and automatic transmission.
These are all somewhat recent features that aren't supported on all
vehicles.